The present invention relates to a novel lymphokine which suppresses platelet activation, to its process of isolation and purification and to medicaments containing it.
It is known that stimulated T cells excrete a certain number of soluble factors among which certain are capable of regulating the functions of effector cells.
It has been demonstrated recently (cf. M. JOSEPH, C. AURIAULT, A. CAPRON, M. VORNG and P. VIENS, NATURE 303:8IO) that blood platelets taken up in rats infected with Schistosoma mansoni, express antiparasite properties destructive in vitro, which increase in the course of the infection. The maximum cytoxicity has been observed when the rats have expressed a high level of immunity with respect to re-infection. This platelet cytoxicity declines rapidly after eight weeks of infection, despite the presence of IgE antibodies in the serum of these infected rats. This is the reason why the inventors have been led to consider that the factors of the T cells, produced after stimulation of suppressor T cells by circulating antigens of S. mansoni, play a role in this diminution, and this mechanism can appear as a regulation in return of immune functions of the platelets in the infection of the rat. In the same way, it has been shown that human platelets can be induced in cytoxic effectors against schistosomules, by incubation with serum rich in IgE of patients afflicted with schistosomiasis or asthmatic allergy patients, the cytoxic process being retarded in the latter case by the addition of anti-IgE or of a specific allergen (cf. M. JOSEPH, J. C. AMEISEN, J. P. KUSNIERZ, V. PANCRE, M. CAPRON and A. CAPRON, 1984, C. R. ACAD. SC. PARIS 298:55).
It is an object of the present invention to isolate a suppressor factor of the activity of the blood platelets, which is capable of playing, among other things, an immunomodulator role of allergic manifestations.
The present invention relates to a factor obtained from T cells stimulated by Concanavaline A or by an antigen, which can inhibit the IgE-dependant platelet cytotoxicity with respect to young larvae of S. mansoni, of greatly diminishing the chemoluminescence of platelets in an IgE-anti/IgE reaction, which is in correlation with the antiparasitic cytotoxicity and of inhibiting platelet activation in non-IgE dependant intolerances, which factor is denoted by the name of lymphokine for the suppression of platelet activation (LSPA) and is produced by T OKT8.sup.+ lymphocytes.